The present invention relates in general to communication systems and in particular to systems and methods for satellite based communication.
Satellite communication systems provide various benefits to consumers of communication services such as for telephony, internet communications, television communications among others. Various satellite systems are currently available, which are discussed below.
Satellites employing a geostationary (GSO) orbit provide the convenience of having one or more satellites in such a system remain fixed in relation to points on the surface of the earth that they communicate with. However, at GSO altitude, which is about 36,000 kilometers (km), communication latency is about 600 milliseconds (ms). Such latency leads to very slow communication throughput and is particularly ineffective for Internet communication. For example, the main page at “www.cnn.com”® would take about 24 seconds to load with this latency period in effect.
For this reason, satellites employing non-geostationary orbits (NGSOs) such as medium earth orbit (MEO) (between 2000 and 36000 km) and low earth orbit (LEO) (below 2000 km) have in certain cases, been used instead. Existing LEO and MEO satellite systems employ inclined orbits to enable such systems to reach high concentrations of customers located in the northern and southern hemispheres. In such orbits, the satellites move continuously with respect to various earth stations with which they communicate. Moreover, successive satellites in such constellations commonly move along different orbits. Thus, many such systems employ omni-directional antennas at earth-based user terminals to enable ongoing communication to take place as the various satellites in a constellation move through their respective orbits. However, such omni-directional antennas have very low gain, thereby limiting the communication throughput (communication bandwidth) achievable using this approach. One way to compensate for the low gain level of the antennas at the user terminal is to significantly increase the power used for satellite antenna transmission. However, such increased satellite transmission power levels may exceed the power available using current satellite power generation technology, and are therefore impractical.
Moreover, satellites in the LEO and MEO systems may employ mechanical tracking or phased array (electronically steerable) antennas for communication with the earth-based based user terminals to communicate therewith. Such antennas are very expensive, thereby imposing a significant premium on the cost of communication services employing LEO/MEO satellite systems. Accordingly, there is a need in the art for satellite communication systems providing effective communication service at a reduced cost.